1. Field of the Invention
The present invention relates generally to an apparatus for recording and reproducing a video signal, and, more particularly, to an apparatus for recording and reproducing a digital video signal which is capable of high speed reproduction of a recorded digital video signal.
2. Description of the Related Art
In an apparatus for recording and reproducing a digital video signal (hereinafter referred to as a digital VTR), the amount of data to be recorded is far more than that in an apparatus for recording and reproducing an analog video signal. Therefore, in the digital VTR, data of an image signal of one field is recorded in plural video tracks of a magnetic tape. For example, in the digital VTR of D-1 format (one of International Standard of the digital VTR), the data of the image signal of one field is recorded in ten video tracks in order to record the video signal of the NTSC Standard. In the D-1 format, prior to recording operation, the data of the video signal is shuffled for every unit of pixel in order to improve the error correction characteristic of the data to be recorded. The shuffled data of the video signal is recorded in the video tracks in the shuffled order.
In a high speed reproducing operation using the data of the video signal recorded as mentioned above, a reproduction image can be formed by using the data of video signal reproduced from the plural video tracks which are not remotely located with respect to each other in the running direction of the magnetic tape. Moreover, since the data of the reproduced video signal is Interpolated in each unit of one pixel, a legible video image may be reproduced. However, in the above-mentioned recording and reproducing apparatus of the digital video signal, the image quality is deteriorated because the data of the video signals of plural fields are mixed in with the data of the video signal in the high speed reproduction operation.
In the high speed reproduction operation in the apparatus of the D-1 format, a digital recording and reproducing apparatus of the video signal for preventing intermingling of the video images of the plural fields in the reproduced image is disclosed in the U.S. Pat. No. 5,130,861. According to this reference, the video signal is converted to synchronizing blocks having a predetermined format, and the synchronizing blocks are recorded in the video tracks. During the reproducing operation, the synchronizing blocks are reproduced by reproducing heads, which are larger than the recording heads. Where the video signal recorded as mentioned above is reproduced at a tape speed of two times or three times the tape speed in recording operation, the entire video signal on the tape are detected by the reproducing heads and are stored in plural memories. Each memory corresponds to each one of plural fields, and a switching means controls the memories so that the data of each field is stored in a predetermined memory. The switching means is activated by detecting the synchronizing block. When a predetermined combination of ID pattern information is completed in the memory, reproduction of the data of the entire image signals of one field is determined, and the data of image signal of one field is output from the memory and is displayed as a video image. Consequently, the displayed video image is formed by the data of the video signal of the same field. As mentioned above, in the digital VTR using the D-1 format, the video image can be formed by the video signal of the same field in the high speed reproducing operation. In the prior art, only a part of the recorded data is produced during a high speed reproducing operation where the tape running speed exceeds ten times the tape running speed in the recording operation. Thus, high speed reproduction of the recorded data is impossible in such a high tape running speed.
Recently, data compression technology has been introduced in the digital VTR in order to reduce the amount of data in recording operation. A reference disclosing such technology is, for example, "An Experimental Study for a Home-use Digital VTR", IEEE Trans. on CE, Vol. 35, No. 3, pp. 450-457 (August 1989 by C. Yamamitsu, A. Ide, A. Iketani, T. Juri, S. Kadono, C. Matsumi, K. Matsushita and H. Mizuki). According this reference, the data in a region of 8 pixels in the horizontal direction and 8 lines in the vertical direction of the video image is defined as a DCT block (discrete cosine transform block), and the DCT block is used as a basic unit in data processing. In the data compression operation, an orthogonal transform operation is applied to the data of the DCT block, and subsequently, variable length coding operation is applied thereto.
The video signal data-compressed as mentioned above is recorded on the magnetic tape of the digital VTR. In the reproducing operation, the data is reproduced in units of one DCT block. When the video image recorded as mentioned above is reproduced at a high speed, the reproduced DCT blocks are intermingled with the DCT blocks having the data of image signals which are different in the recorded time. Therefore, a video image at a part in the video display is different from a video image at another part in the video display in the recorded times, and, as a result, an unsightly image is reproduced. The deterioration of the reproduced image is caused by the data compression in the recording operation and data interpolation in the reproducing operation. Namely, it is caused by an interpolation of the data block that is different from the original data with respect to a point of time. In general, when the data compression is applied in the recording operation which is operated in units of one data block, such as the DCT block, the lost data can not be interpolated with data which is located adjacent to the lost data in the video image, and the data which is used for the interpolation is different from the lost data adjacent in the time sequence such as data in the previous field or frame. The time difference between the lost data and the interpolation data increases as the speed ratio of a reproducing speed to the recording speed increases, and therefore, the quality of the reproduced image is further deteriorated.